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(a) Schematic illustration of an experimental set-up with a four-electrode arrangement routinely used in ion transport routine experiments. The membrane can contain either symmetric or asymmetric channels. (b) Left – characteristic linear I–V curve for a membrane with symmetric nanochannels. Under a surface-charge-governed regime, the response is strongly dependent on the surface charge. High concentration of surface charges leads to high conductance (steep slope). Right – characteristic I–V curve with a rectifying behavior for a membrane containing asymmetric nanochannels. Under a surface-charge-governed regime, the response is strongly influenced by the surface charge. Higher surface charge leads to higher rectification efficiency (ratio between I (high conductance branch) and I (low conductance branch))
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Advanced nanostructured membranes with high ion flux and selectivity bring new opportunities for generating clean energy by exploiting the osmotic pressure difference between water sources of different salinities.
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Citations
... In recent decades, the energy crisis has become a growing concern. Although the development of renewable energy sources, such as solar energy, wind energy, and tidal energy (Laucirica et al., 2021), has alleviated this problem to a certain extent, the collection and use of these clean energy sources are still limited by weather, geography, and time of the year. The osmotic energy, called "blue energy," which has received extensive attention from researchers due to its advantages of large storage capacity, non-pollution and sustainability. ...
Osmotic energy harvesting was a promising way to alleviate energy crisis with reverse electrodialysis (RED) membrane-based technology. Charged hydrogel combined with other materials was an effective strategy to overcome problems, including restricted functional groups and complicated fabrication, but the effect of the respective charges of the two materials combined on the membrane properties has rarely been studied in depth. Herein, a new method was proposed that charged hydrogel was equipped with charged filter paper to form dual network fiber-hydrogel membrane for osmotic energy harvesting, which had excellent ion selectivity (beyond 0.9 under high concentration gradient), high ion transference number and energy conversion efficiency (beyond 32.5% under wide range concentration gradient), good property of osmotic energy conversion (∼4.84 W/m² under 50-fold KCl and ∼6.75 W/m² under simulated sea water and river water). Moreover, the power density was attributed to the surface-space charge synergistic effect from large amounts overlapping of electric double layer (EDL), so that the transmembrane ion transport was enhanced. It might be a valid mode to extensively develop the osmotic energy harvesting.
... This capability inspired the scientific community to develop SSN devices that can tune and control the movement of ions by different stimuli, harnessing the potential of responsive ion transport in diverse applications ranging from chemical fluidic actuation [9][10][11][12] to biosensing, [13][14][15][16] and from nanoelectronics to energy conversion systems. [17][18][19][20][21][22] Up to now, it is well-known that ion transport through SSNs (and consequently, iontronic output) is mainly determined by the channel geometry and the physicochemical properties of the channel surface. 23,24 For instance, if the channel aperture is in the nanometric range, the ion enrichment generated by the surface charges determines an ion transport governed by the surface charge density. ...
... While these equations were derived in conditions that, in principle, are not compatible with the case of study of this review (channels with nanocurvature, not flat surface), the trends and qualitative behaviors observed in Debye-Hückel are still representatives in more complex systems. 19,38 In the case of charged nanochannels, it is assumed that if the aperture radius is in the order of l D , the counterion enrichment due to the surface electrostatic potential promotes ion concentration polarization in the inner volume of the nanostructure. Thus, working with low/moderated electrolyte concentrations where the surface charges are not effectively screened enables the development of selective ion transport characteristics. ...
... Details on the different nanofabrication methods can be found in previous review articles and books. 18,19,25,36 Silicon-based nanochannels and nanoslits can be created by different nanofabrication protocols. 31,79,80 One common method is the sacrificial layer method which includes optical lithography and chemical treatments and results in silica nanoslits connected with two microchannels (the fluidic reservoirs). ...
Nanofluidic field-effect transistors for tailored transport and bio-inspired functionalities: solid-state nanochannels can be smartly tuned by external potentials to induce open/closed states or promote ion selectivity in the same way as biological ion channels.
... Typically, the characteristic length of EDL is called "Debye length" and it takes values of a few nanometers in electrolyte solutions of low and moderated concentrations (e.g., B3 nm in aqueous 0.1 M KCl at 298K). Then, in the case of charged SSNs with a size comparable to the Debye length exposed to an electrolyte solution, the inner volume of the pore/channel will be enriched with counter-ions and this effect will play a central role in the features of the iontronic output [3,39]. In this context, the ion transport across the pore/channel is surface charge-governed, and it is possible to obtain information about its magnitude by analyzing the IÀV curves. ...
... Over the last ten years or so, numerous studies have focused on the synthesis of new membranes and their improvement to overcome this barrier [13][14][15] are characterized in the labs by the power per unit area (power density) on devices with a membrane area of the order of 10 µm 2 , assuming that for given fluids, the power density depends only on the membrane material and thickness, and will be poorly affected by the scale-up. This is justified by the assumption that the measured resistance in the experimental device corresponds to the one of the most resistive object, i.e. the membrane. ...
Blue energy represents a large reservoir of renewable osmotic energy that can be converted into electricity by reverse electrodialysis (RED). This method is based on ion-exchange membrane. Before large scale production, these membranes are compared on very small samples on the basis of the power they enable to produce per unit area. Through a systematic study of the effect of the membrane size on the power density, we show experimentally that for classical measurement cells, the power density strongly varies with the size of the membrane: the smaller the membrane, the higher the power density. The results are explained by a theoretical modeling which describes the effect of the access resistance at the scale of the membrane. Based on this work, a few recommendations are formulated to perform scalable and meaningful measurements of membrane resistance and power density.
... Electrostatics plays a key role in the reactivity of particles and (bio) interfaces, e.g. colloid stability [1], ion adsorption [2], electrokinetics [3], polyelectrolyte swelling [4], cell biology [5][6][7], or blue energy harvesting [8]. Accordingly, modelling the electrostatics of charged interfaces and particles is of paramount importance, and formalisms reported for that purpose include the well-known mean-field Poisson-Boltzmann (PB) theory [9] and extensions thereof [10][11][12][13][14][15][16][17][18][19][20][21][22], and advanced molecular simulations [2,[23][24][25][26][27]. Electrostatics of so-called soft colloids, i.e. colloids that consist partly or entirely of ionpermeable polyelectrolyte-like material with 3D distributed structural charges (e.g. ...
When a charged layer decorating a particle or a macroscopic surface is equilibrated with an electrolyte solution, a constant Donnan potential is established through that layer due to charge-driven accumulation of counterions and companion exclusion of coions. This situation arises when the thickness of the surface layer well exceeds the screening Debye length, a condition derived from mean-field Poisson-Boltzmann theory within point-like charge approximation. Herein, we revisit this condition underlying the applicability of Donnan electrostatic representation with the account of steric effects mediated by the sizes of the electrolyte ions and structural layer charges. A transcendental equation is derived for the Donnan potential as a function of sizes and valences of anions and cations, electrolyte concentration and size of the layer charges, and a closed-form expression is provided for symmetrical electrolytes. Therefrom we evidence that the existence of a Donnan potential is conditioned not only to large values of the layer thickness compared to a here-defined Debye length operative within the shell, but to additional verification of a criterion that involves space charge density of the layer, solution ionic strength and electrolyte nondiluteness parameter. Illustrative computational examples show how the existence and magnitude of the Donnan potential depend on the key molecular descriptors of the electrolyte and soft interface, and they further quantify the deviations from predictions based on classical Donnan potential expression valid for dilute electrolytes.
... Examples include filtration of water to remove contaminants such as oil 6 and dyes, 7 nanopore sensors for single molecules, 8 proteins, 9 blood sugar, 10 and drugs 11 as well as DNA, 12 ssDNA, 13 and protein sequencing. 14 The potential of using nanofluidic devices based on nanopore membranes for novel applications such as power generation 15 and electroosmotic pumps 16 has also been explored in detail. ...
... 33,34 Furthermore, translating the performance of single pores to multipore systems without losing performance has proven to be challenging. 15,35 Different techniques like e-beam lithography, 36 ion beam sculpting, 17 e-beam drilling using a transmission electron microscope, 37 focused ion beam drilling, 38 dielectric breakdown, 39 or laser-assisted pulling 40 can only be used to fabricate a single or few nanopores and thus lack the scalability that many applications require. Additionally, these techniques do not allow to precisely shape the geometry of the pores. ...
... To do this, it will be assumed that tip size and surface charge will be the same, as similar values have been reported in other systems. 15 The only differences stem from the cone angle and pore length. ...
... The commercial benchmark of maximum power density is 4-6 Wm −2 . Several porous membranes having potentials of scaling up have surpassed this benchmark in laboratory investigation using a working area below 0.1 mm 2 [118]. It is extremely important to use a larger working area in order to estimate a practically attainable combination of energy efficiency and maximum output power density. ...
In recent years, the utilization of the selective ion transport through porous membranes for osmotic power generation (blue energy) has received a lot of attention. The principal of power generation using the porous membranes is same as that of conventional reverse electrodialysis (RED), but nonporous ion exchange membranes are conventionally used for RED. The ion transport mechanisms through the porous and nonporous membranes are considerably different. Unlike the conventional nonporous membranes, the ion transport through the porous membranes is largely dictated by the principles of nanofluidics. This owes to the fact that the osmotic power generation via selective ion transport through porous membranes is often referred to as nanofluidic reverse electrodialysis (NRED) or nanopore-based power generation (NPG). While RED using nonporous membranes has already been implemented on a pilot-plant scale, the progress of NRED/NPG has so far been limited in the development of small-scale, novel, porous membrane materials. The aim of this review is to provide an overview of the membrane design concepts of nanofluidic porous membranes for NPG/NRED. A brief description of material design concepts of conventional nonporous membranes for RED is provided as well.
... As a result, researchers are exploring better, renewable, and clean options including sun, wind, heat, wave, water, and water concentration gradient to remedy this problem [14][15][16][17][18][19]. Meanwhile, researchers have been considering the method of exploiting the difference in water concentration because of its novelty and appeal [20][21][22][23][24]. ...
Energy production is one of today's most pressing issues. Finding alternative energy sources has become one of the hottest research areas for scholars due to the limited use of fossil resources. Using water sources of different concentrations is one of the newest methods of energy production. Due to the energy of mixing fluids, two fluids of different concentrations on both sides of a nanochannel membrane can produce energy. Given the costs and restrictions of studying complex systems experimentally, simulation is required to investigate their behavior and determine the best states. As a result, using an energy production strategy, this work explores the effect of nanochannel shape on the ion transfer behavior. Asymmetric (bullet, trumpet, cigarette, hourglass, and hill) and symmetric (cylindrical) geometries were utilized. The effects of different geometries, soft layer density, and concentration ratio on energy production considering the effect of ion partitioning in soft surfaces was investigated. A finite element numerical computation approach was employed to solve the Poisson-Nernst-Planck and Navier-Stokes equations at steady-state. The best geometry at various concentration ratios to create the most performance were: cylindrical and cigarette for osmotic current, hourglass and trumpet for transmission number, hourglass and trumpet for diffusion potential, cylindrical for electrical conductivity, cylindrical and trumpet for power capacity, and hourglass and trumpet for energy conversion efficiency, respectively. In the case of considering the ion partitioning at a concentration ratio of CH/CL=1000for trumpet geometry, raising the soft layer's charge density from NPEL/NA=25to 100mol/m3 boosted the maximum produced power by about 25 times, from 0.215pW to 5.35pW.
... Thus, constructing nanofluidic membranes with high pore densities is crucial for nanofluidic RED (NRED) systems, and several large-scale nanofluidic membranes have been developed to address the issues. Table 2 categorizes scaled-up nanofluidic membranes with high pore densities into 1D multipore membranes, 2D-layered membranes, 3D nanoporous membranes, and mixed-dimensional membranes [94,95]. With the recent emergence of 2D materials, such as graphene oxide (GO), MXene, and molybdenum disulfide (MoS 2 ), various 2D-layered membranes consisting of stacked 2D nanosheets with nanochannel array among the membranes have been fabricated to overcome the limitations of conventional IEMs [62,63,67,69,75]. ...
Reverse electrodialysis (RED) is an emerging renewable energy technology that generates electricity by combining concentrated and diluted streams with varying salinities. Ion-exchange membranes (IEMs) have undergone significant advancements in RED, with an enhanced understanding of system configuration and operation conditions for increased power generation. This comprehensive review focuses on recent advances in IEMs, process design, and optimization of RED systems over the last five years. Challenges in the pilot-scale and field-scale systems are discussed, as well as practical limitations such as IEM fouling and electrochemical reactions on electrodes. Future research directions for enhancing overall performance, power generation, and economic feasibility of RED for salinity gradient power (SGP) generation are also proposed. Future advances in the following directions will increase the economic feasibility of RED application in SGP: 1) development of scalable IEMs with high anti-fouling efficiency, mechanical strength, and ion selectivity/conductivity, 2) process optimization (including pre-treatment) for IEM and electrode fouling mitigation, and 3) control of undesirable irreversible faradaic reactions.
... According to Laucirica et al., 48 the membrane potential Em of the ion-selective nanoporous membrane is given by ...
The ion transport measurements using various ion-exchange membranes (IEMs) face several challenges, including controllability, reproducibility, reliability, and accuracy. This is due to the manual filling of the solutions in two different reservoirs in a typical diffusion cell experiment with a random flow rate, which results in the diffusion through the IEM even before turning on the data acquisition system as reported so far. Here, we report the design and development of an automated experimental setup for ion transport measurements using IEMs. The experimental setup has been calibrated and validated by performing ion transport measurements using a standard nanoporous polycarbonate membrane. We hope that the present work will provide a standard tool for realizing reliable ion transport measurements using ion-exchange membranes and can be extended to study other membranes of various pore densities, shapes, and sizes.
